1. Field of the Invention
The present invention relates to a substrate polishing apparatus, and more particularly to a substrate polishing apparatus capable of improving measurement accuracy of a substrate measuring device which is incorporated in the substrate polishing apparatus.
2. Description of the Related Art
In a semiconductor fabrication process, a substrate polishing apparatus is used to polish a surface of a substrate such as a semiconductor wafer to a flat and mirror surface. The substrate polishing apparatus has a rotatable table (polishing table), and a substrate is pressed against a polishing surface on the rotatable table. Then, while a polishing abrasive is supplied onto the polishing surface, the rotatable table is rotated to polish the substrate. There has been proposed a substrate measuring device utilizing light as a device for measuring a film on a substrate during polishing the substrate. For example, a film thickness can be measured to determine an end point of polishing based on the measured film thickness.
There has been proposed a stream-type device as this type of substrate measuring device. For example, Japanese laid-open patent publication No. 2001-235311 discloses a substrate measuring device having a water supply passage provided in a rotatable table. An outlet of the water supply passage is provided in the polishing surface, and pure water is ejected through the water supply passage to the substrate. Two optical fibers are disposed in a stream. Measurement light is emitted through one of the optical fibers to the substrate, and reflected light is received through the other of the optical fibers from the substrate. Then, the film thickness is calculated based on the reflected light.
In the above substrate polishing apparatus, the substrate is polished in the presence of the polishing abrasive between the substrate and the polishing surface. When the polishing abrasive flows into the pure water supplied through the water supply passage, the transparency of the pure water is lowered. As a result, an amount of the reflected light that has been received is lowered. Therefore, it has been a task for the stream-type measuring device to prevent the pure water from being mixed with the polishing abrasive or keep the transparency of the pure water to such a degree that the measurement is not affected even when the polishing abrasive flows into the pure water.
The above substrate polishing apparatus has several expendable components. One of the expendable components is a light source component for emitting measurement light. The light source component comprises a lamp, for example. The lamp has a service life of about four months, for example, although the service life varies depending on the type of lamp and condition under which the lamp is used. The substrate polishing apparatus may have a control valve disposed in the water supply passage for controlling water-injection timing. In this case, the control valve may be one of the expendable components.
The expendable components are usually embedded in the polishing table. For example, the expendable components are disposed inwardly of a skirt which is provided along an outer edge of the polishing table.
The expendable components are required to be replaced at regular or irregular intervals. In a replacing operation, an operator puts a hand into the skirt of the polishing table from below the skirt, and then replaces the expendable components. However, it is difficult for the operator to reach the expendable components, and hence the replacing operation is not easy to accomplish.
The stream-type substrate measuring device described above supplies water into a through-hole formed in a polishing pad, so that slurry flowing between the polishing table and the substrate into the through-hole can be diluted, and that the slurry attached to the substrate can be cleaned. Thus, influence on measurement from the slurry is reduced to maintain a required capability of measurement.
However, a large amount of water should be supplied in order to maintain a required capability of measurement. When a large amount of water is supplied, the water flows to the polishing surface on the polishing table to cause the slurry to be diluted. Dilution of the slurry may have an influence on the characteristics of the polishing capability. Heretofore, as described above, if the amount of water is increased in consideration of the measuring capability, the polishing capability is lowered, and there is a trade-off relationship between the measuring capability and the polishing capability.